CU-Boulder scientists contribute to key discovery on moon of Saturn

Hydrothermal activity on icy Enceladus hint at environment suitable to life

By Charlie Brennan

Staff Writer

Posted:
03/11/2015 02:00:00 PM MDT

Several distinct plumes of water ice can be seen spewing out from Saturn's moon Enceladus in this dramatically illuminated image recorded by the Cassini spacecraft. (Courtesy photo / NASA)

University of Colorado scientists working on the Cassini mission to Saturn with an international team of partners have discovered hydrothermal activity on one of its icy moons suggestive of an environment suitable for life.

The CU contributors to the findings are based at the university's Laboratory of Atmospheric and Space Physics, and their discovery is featured in a paper published today in the journal Nature.

LASP research associate Sean Hsu is lead author on the paper, which focuses on microscopic grains of rock found in plumes, or geysers, emanating from the Saturn moon of Enceladus.

Hsu emphasized that evidence of an environment suitable for living organisms is not proof of their presence on Enceladus, one of at least 60 moons or so-called moonlets.

"The fact that you have hyrdothermal systems, which will bring energy, nutrients and, of course, liquid water... it's still not clear the time scale that this system has been existent, and how stable that is," Hsu said.

"That is one big uncertainty regarding this kind of question. Even if you have all three of those elements, it's not a guarantee that there will be a lifeform."

LASP's Larry Esposito is the principal investigator on a $12.5 million Ultraviolet Imaging Spectrograph on board the Cassini spacecraft, which launched in 1997 and entered the Saturn system in 2004.

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Cassini first showed active geology on Enceladus in 2005, manifesting as icy sprays from the moon's south polar region, and higher-than-expected temperatures in its icy surface. The mission subsequently revealed towering plumes of water ice and vapor, salts and organic materials emanating from fractures in the moon's surface.

Four years of analysis of data from Cassini's Cosmic Dust Analyzer paired with laboratory experiments and computer simulations, have led scientists to conclude that tiny grains of rock in the geysers of Enceladus are likely produced by hot water containing dissolved minerals in the rocky moon's interior that travel upward and encounter cooler water.

"The surface of the moon is more than 90 percent water and ice — maybe 95 percent — and the rings are water ice particles, so it's surprising then that these (grain) particles' composition is not water ice," Hsu said. "That brings us the first attention there might be something different going on."

LASP's Sascha Kempf, an assistant professor in physics and co-investigator on Cassini, is another co-author on the Nature paper.

"Ten years ago it was a big mystery why the nano-grains (in the plumes) were made of silica rather than water ice," Kempf said in a news release. "Now we know the observations were correct. We know where the silica particles are coming from, and why we are seeing them. We learned something very unexpected, which is why I really like this study."

"Dust astronomy," Hsu said, is valuable not only for what it can tell scientists about the dynamics of other celestial bodies, but about our own.

"It's already surprising enough that it is happening on such a small moon," Hsu said. "If we can further explore that kind of system, it would be a great comparison for hydrothermal systems on Earth. Even though we do not find life there, I think that will be a good improvement of knowledge about life as well as solar system formation".

CU professor Mihaly Horanyi is also a co-author on the paper, to which scientists in Germany and Japan also contributed.

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